Different diseases are known, in which the normal operation of the heart is disrupted by aberrant conduction paths in ventricles, such as the atrium, which can cause serious physical problems.
One of the best known of these diseases is atrial fibrillation, which affects several million people per year at least temporarily in the US alone. The aberrant conduction paths mentioned above occur in the atria of the heart so that electrical signals, which control the musculature of the atria, circulate and for example stimulate the muscles at such a high frequency that the regular pumping activity of the atrium no longer takes place.
This means that the pumping activity of the heart is generally reduced without the atrial contribution. Also the blood flow in the atria decreases, so that blood clots can form, which are then transported in the circulation through the body. Finally it is possible for the heart rate to increase, when electrical signals are conducted to the heart at too high a frequency. Arrhythmias can then result.
The reason for the occurrence of aberrant conduction paths in the atrium or in the right or left ventricle is frequently damage to the inner walls of the chambers, for example due to ischemia or inflammation. The damaged tissue has different electrical properties and conducts the electrical signals more effectively. Of significance is the formation of so-called reentry circuits, in which the stimulus circulates, and ectopic foci, which generate pulses at high frequency outside the normal stimulus formation system (sinus node, AF node, etc.). Ectopic foci are generally located in the region where the pulmonary veins open into the atrium.
In order to treat such diseases, such as atrial fibrillation, it has been proposed that the aberrant conduction paths should be interrupted by ablation and the ectopic foci should be isolated. A high-frequency catheter for example can be used for this purpose, being positioned on the inside of the chamber wall and modifying this by specific application of an alternating current, so that electrical conductivity is reduced. An attempt is hereby made to isolate the openings of the pulmonary veins specifically from the remainder of the atrium. The problem arises here of assessing whether the treatment was successful or how likely it is that atrial fibrillation will recur. Diagnostic questions are also relevant, when for example methods are sought for determining the course of conduction paths.
To assess a therapeutic treatment of atrial fibrillation, it was proposed in the article “Detection of Pulmonary Vein and Left Atrial Scar after Catheter Ablation with Three-dimensional Navigator-gated Delayed Enhancement MR Imaging” by D. C. Peters et al., Radiology, Volume 243, 2007, page 690-695, that so-called delayed enhancement recording technology should be used to show up scars resulting from high-frequency ablation of the right atrium. It is proposed here that the proportion of the periphery of the atrium ablated should be determined as an assessment variable.
The delayed enhancement imaging method is described in more detail by U.S. Pat. No. 6,205,349 B1. After a magnetic resonance contrast agent has been administered here, there is a delay for a predetermined time period before T2-weighted magnetic resonance image data is recorded, in which damaged myocardial tissue can be clearly distinguished from normal myocardial tissue.
In a different approach US 2010/0160765 A1 and US 2010/0160768 A1 describe a method for determining the likelihood or risk of recurrence. It is proposed here that a global parameter should be determined, for example the ratio of ablated surface to non-ablated surface or the ratio of diseased to healthy tissue, with an increased likelihood of recurrence being assumed when a limit value is exceeded.
When assessing a treatment and also for diagnostic approaches however the described methods fall short, as they only consider the ablated surface or distance on a periphery around the pulmonary veins globally. This does not exclude the possibility of still-functioning aberrant conduction paths being present, as a narrow strip is sufficient for these. It should also be noted here that it is complex and generally barely possible for a diagnosing physician to make an image-based assessment, as possible conduction paths are very difficult to identify in the reconstructed slice images.
US 2008/0077032 A1 relates to methods, which provide diagnostic information and use endocardial surface data of a heart of a patient. In this process a model of the endocardial surface is used to determine measurements which have diagnostic relevance, for example the three-dimensional partial shortening of the left ventricle. Other examples allow characteristic variables of heart movement to be determined from heartbeats. It is also discussed in conjunction with pacemakers that the electrical progression of signals can be modeled, by applying an initial stimulus at a specified location of a network model.
An article by Olaf Dossel et al., “A Framework for Personalization of Computational Models of the Human Atria”, 33rd Annual International Conference of the IEEE EMBS, Boston, Massachusetts USA, 2011, page 4324-4328, relates to the step by step personalization of a calculation model for human atria. First CT or magnetic resonance data is used to create an anatomical model, over which a fiber structure is placed on the basis of a rule-based method. Late enhancement magnetic resonance imaging is proposed for displaying fibrotic tissue. Regions with a high signal level segmented there can be input into the geometric model of the atrium as additional labels.